Mr. Pendanski always likes to come across as a nice guy, someone who respects the boys at the camp, yet his behavior towards Zero tells a different story. For no apparent reason, he constantly subjects Zero to what can only be described as bullying: verbally abusing him, belittling him, and singling him out for ridicule.
Perhaps Pendanski has it in for Zero because he's an easy target. Unlike the other boys, he isn't physically strong or aggressive in any way. Bullies like Pendanksi can sense such vulnerability from a mile away like a shark can smell blood. Like just about all the adult authority figures at the camp, Pendanski also appears to be on a massive power-trip and loves nothing more than to exercise control over someone he knows won't talk or fight back.